The practice of sharing syringes without adequate sterilisation between successive users is a major contributor to the transfer of Human Immunodeficiency Virus (HIV) and Hepatitis with subsequent severe repercussions for the sufferer and at a high cost to society for supporting and providing medical attention to sufferers.
In response to this problem, syringes have been developed with the aim of preventing syringe re-use.
A particular problem associated with syringes is needlestick injury to the user.
One solution has been to develop syringes where the needle is permanently retractable into the barrel of the syringe, retraction driven by a compressed spring, as for example described in International Publication WO 01/80930.
Although very effective, retractable syringes are relatively expensive, particularly when required in large quantities for mass immunizations or for distribution to intravenous drug users. This is particularly a problem in third world countries where the incidence of HIV is high, mass immunization programs need to be frequently undertaken and healthcare resources are limited.
There is therefore a need to produce a syringe that automatically prevents or minimize the risk of syringe re-use and/or needlestick injury and that is relatively inexpensive to produce.
With this need in mind, syringes with non-retractable needles have been developed, wherein a cover or sheath is activated to cover the needle after syringe use.
In this regard, reference is made to U.S. Pat. No. 6,086,566 and 6,428,519 which describe a movable needle cover A particular feature of these prior art syringes is that they are relatively complicated, each requiring a guiding member to assist guided movement of the cover over the needle and also to positively retain the movable cover in its protection position over the needle.
Reference is also made to U.S. Pat. No. 6,565,540 which describes a spring actuated, movable needle cover. A disadvantage of this syringe needle cover is that the spring is gradually compressed during plunger depression, which provides an unacceptable “feel” to the syringe user and hence detracts from the commercial attractiveness of the syringe.